Optical clearing of synthetic opals: a fluid kinetics study using optical coherence tomography

A non-contact method for assessing the local geometrical thickness, porosity, and effective refractive index of synthetic opals using spectral optical coherence tomography is proposed. This approach was employed to investigate the diffusion of aqueous glycerol solutions with varying concentrations into the macropores of synthetic opals pre-filled with water. The kinetics of changes in the optical thickness and refractive index of synthetic opals during the optical clearing process were monitored. The obtained data were analyzed using the least-squares method, which enabled the determination of porosity 20–30%, refractive index 1.37–1.45, and geometrical thickness 0.94–1.17 mm of the synthetic opals. The results were validated by an alternative method of refractive index matching. It is demonstrated that the proposed approach can be applied to the analysis of local structural and optical parameters of porous materials, offering promising prospects for applications in materials science and bioengineering.